Monitoring of the level of glucose or other analytes, such as lactate or oxygen, in certain individuals is vitally important to their health. High or low levels of glucose or other analytes may have detrimental effects. Monitoring of glucose is particularly important to individuals with diabetes. Diabetics may need to monitor glucose levels to determine when insulin is needed to reduce glucose levels in their bodies or when additional glucose is needed to raise the level of glucose in their bodies. In non-diabetic individuals, it may be important to monitor glycemic responses to determine whether therapeutic approaches may be useful to prevent the onset of diabetes.
Analyte monitoring systems may be designed to test blood samples taken periodically and measured outside of the body (in vitro testing), such as by putting a drop of blood on a test strip, and performing an analyte analysis on the test strip. Blood may be taken from a finger (by performing a “fingerstick”) or other locations on the body, such as the arm, thigh, etc. Tests performed in such a manner may be referred to as “discrete” measurements, and in the case of glucose measurements, “blood glucose” (BG) measurements. Other systems are designed to measure analyte levels within the body (in vivo), using a suitable sensor, without drawing blood for every measurement. Certain systems have combined functionality for performing both sensor-based as well as discrete measurements.
In some situations, it is medically desirable to monitor analyte levels in a subject closely, over a substantial period of time, or on an ongoing basis for an extended time period, in some cases indefinitely. A monitor that tracks glucose levels by automatically taking periodic in vivo measurements, e.g., one measurement per minute, or more or less frequently, is known as a “continuous glucose monitor” (CGM). Prior art CGMs have been provided, for example, in the form of a system. A portion of the system, comprising an electrochemical sensor partially inserted into the skin, and an associated processor and transmitter, with a self-contained power supply, is attached to the body of the user and will remain in place for an extended period of hours, days, weeks, etc. The transmitter takes analyte measurements periodically and transmits them, for example, by short-range radio communications, to a separate receiver/display device. The receiver/display device will typically receive discrete BG measurements (e.g., from a separate BG meter or an included BG test strip port), as well as a port, such as a USB port, for communications with upstream computers and/or other electronics. In some embodiments, the receiver unit may be directly or indirectly interfaced with an insulin pump, for managing the subject's insulin therapy.
The accuracy of the analyte measurements obtained with an in vivo sensing system is important. Calibration of such systems may be performed by comparing in vivo “system” measurements against discrete BG “reference” measurements from fingerstick samples measured on a test strip.
CGM systems typically perform calibrations on a fixed schedule. However, such a fixed schedule may impose inconvenience on the user if a required calibration occurs when a user is occupied with other activities or asleep. In some instances a required calibration may occur when analyte levels are in a state of instability or rapid change. Calibrations taken during such times of unstable analyte levels may sometimes provide less than optimal results. Accordingly, it would be desirable to provide calibration routines which allow customization by user. It would also be desirable to provide calibration routines which calibrate when the analyte levels and rates of change are more desirable for accurate measurement and observation.